harness: ensure files and timer are properly cleaned up
harness: ensure files and timer are properly cleaned up

Moving before(), after() and startTimer() into Run() allows us to use
defer to ensure resources are properly cleaned up after execution.

glevand/coreos--mantle,quantum/coreos-mantle,dm0-/mantle,glevand/coreos--mantle,marineam/mantle,marineam/mantle,dm0-/mantle,quantum/coreos-mantle